I'm looking at upgrading my focusing rail. I have a dual axis (http://www.adorama.com/mcfrs.html), but hardly ever use the Y axis, and would like to have Arca plate/QR built-in. I shoot with gripped 5DsR, Zeiss 100 MP, extension rings, MP-E 65, occasionally Canon 180M, with MT-24 EX. So a rather...